Our long-term objective is to understand the complex interrelationship between phospholipid, sphingolipid metabolism and metabolic signaling in vivo. Intermediates of phospholipid (PL) and sphingolipid (SL) metabolism serve as second messengers for a number of signaling cascades including activation of G-protein-coupled receptors such as adrenaline, thrombin, etc., as well as receptor tyrosine kinases by growth factors. They mediate a number of processes ranging from protein secretion to activation of apoptosis. We have initiated studies to understand different aspects of lipid signaling in Drosophila. Lipid Reservoirs and Signaling.Sphingomyelin is a reservoir for several lipid messengers such as ceramide, ceramide 1-phosphate, sphingosine, and sphingosine 1-phosphate. We have initiated a study to delineate the in vivo role of membrane-bound neutral sphingomyelinase in Drosophila and to understand the importance of the sphingomyelin cycle in regulation of cell growth. To this end, we have identified the Drosophila sphingomyelinase, generated antibodies, obtained transgenic flies expressing both genomic and cDNA copies of sphingomyelinase, and initiated a genetic screen using western analysis to isolate sphingomyelinase mutant flies.Lipid Distribution and Signaling.PL and SL at the plasma membrane play an important role in stimulus-response coupling, cell differentiation, movement, and exo- and endocytosis. They are asymmetrically distributed in biological membranes, and different proteins catalyzing uni- and bi-directional movements of lipids perpetuate asymmetry. Our current efforts focus on scramblase, a protein proposed to be involved in bi-directional transbilayer movement of phospholipids. We have recently completed a genetic screen and obtained Drosophila flies lacking a scramblase protein. We have begun phenotypic analyses of these mutant flies. We anticipate that a combination of genetic, molecular, and biochemical approaches in Drosophila will define the important players involved in PL, SL signaling in their normal cellular environment.